The report also highlighted the 10 areas with the largest upper-income populations, which were mostly in the northeast region or on the California coast.

"Midland, Texas, the exception to this rule, leads the metropolitan ranking of upper-income areas," Pew reported. "Some 37% of the adult population in Midland was upper income in 2014, thanks to a prospering oil economy."

Pew defined upper-income households as those with an income that is more than double the US median household income. Incomes are adjusted for household size and for the cost of living in the area relative to the national average cost of living. "That means the incomes of households in relatively expensive areas, such as New York-Newark-Jersey City, NY-NJ-PA, are adjusted downward," Pew explained in its methodology.

Note that New York City didn't crack the top 10. In addition to Pew adjusting incomes for the cost of living, it's important to recognize that New York City, with a population of about 8.5 million, makes up less than half of the New York-Newark-Jersey City metro area, which has a population of about 19.8 million.

Read on to see which other metro areas joined Midland in the top 10. We included the share of the population that qualifies as upper-income in each metro, along with the median household income of the upper class (also from Pew).